1. Field of the Invention
This invention relates to aqueous liquid lubricant compositions suitable for forming a coating containing an organic binder material on metal surfaces that are coated with a layer of the liquid composition and then dried without rinsing, so that the solids content of the aqueous composition forms on the metal surface a solid layer that lubricates the surface during subsequent cold working operations. The solid film thus deposited is protective against mechanical damage during cold working of the underlying metal. The metal surface processed as described above may or may not have other surface layers, such as phosphate or chromate conversion coatings, coatings formed by anodization, complex oxoide layers such as those that can be formed with a commercially available product named BONDERITE.RTM. 770X from the Parker Amchem Div. of Henkel Corp., Madison Heights, Mich., or the like, underlying the coating produced on the surface by using this invention. The invention is particularly suited to the pointing and drawing of thick walled metal tubes, particularly steel tubes.
2. Statement of Related Art
The basic conventional method for reducing the diameter and wall thickness of metal tubing by cold working is known in the art as "drawing". In drawing, a material harder and stronger than the metal being processed is used as a mandrel inside the tube, to prevent wall thickening that would otherwise occur if tubing were simply pulled, with no mechanical restraint except at its ends. When substantial reductions in outside diameter are to be achieved, it is known in the art to precede the drawing operation itself with another process called "pointing". In pointing, a hard and strong material that shapes the metal tubing being processed is used in the form of a die outside the tubing being worked, almost always completely surrounding it. Reduction of tube diameter with an increase in wall thickness normally occurs when ductile metal tubing is forced through a pointing die with an inside diameter smaller than the outside diameter of the metal tubing being processed. Thus pointing is almost always followed by drawing.
Pointing usually accomplishes a greater proportionate reduction in outside diameter than does drawing, but the total amount of metal movement and the speed, friction, and heat generated are usually greater in drawing than in pointing. Thus the two operations have different minimum requirements for lubricants: Many lubricants that are adequately protective for drawing have been found to be inadequate for pointing, and it is also possible, although less common, for lubricants suitable for pointing to be inadequate for drawing.
Many aqueous liquid compositions that form coatings on metal surfaces that protect the metal surface while it is being cold worked are known. The previously most effective ones have generally been zinc and/or sodium soaps applied over a preceding heavy phosphate conversion coating. (Normally, a sodium stearate or other sodium soap salt is applied over a zinc phosphate coating. Reaction between the sodium soap and the zinc in the zinc phosphate coating is believed to result in both zinc soap and sodium soap layers.) However, this combination is environmentally disadvantageous, because the liquid compositions used to form phosphate coatings generally contain some types of metal ions, such as those of zinc, nickel, manganese, and/or the like, that are regarded as polluting, and the phosphate ions themselves, which are required in phosphate conversion coating forming liquid compositions, are environmentally undesirable in waste waters because of their promotion of eutrophication of natural bodies of water. Zinc soaps are substantially insoluble in water, but cause workplace nuisances at best and hazards at worst because they tend to form fine dust particles in the air around sites of cold working processes when used as cold working lubricants.